WO2023276788A1 - Binder composition for electrochemical elements, electrically conductive material dispersion for electrochemical elements, slurry for electrochemical element electrodes, electrode for electrochemical elements, and electrochemical element - Google Patents

Abstract

The purpose of the present invention is to provide a binder composition able to form an electrode in which an increase in internal resistance can be suppressed following electrochemical element cycles. This binder composition contains a polymer X, N-methyl-2-pyrrolidone, and a nitrogen compound other than N-methyl-2-pyrrolidone. The polymer X contains a nitrile group-containing monomer unit and also contains an aliphatic conjugated diene monomer unit and/or an alkylene structural unit. The molecular weight of the nitrogen compound is 1000 or less. In addition, the HSP distance (RA) between the nitrogen compound and the polymer X is 10.0 MPa1/2 or less.

Description

Binder composition for electrochemical element, conductive material dispersion for electrochemical element, slurry for electrochemical element electrode, electrode for electrochemical element, and electrochemical element

The present invention relates to a binder composition for electrochemical elements, a conductive material dispersion for electrochemical elements, a slurry for electrodes of electrochemical elements, an electrode for electrochemical elements, and an electrochemical element.

Electrochemical devices such as lithium-ion secondary batteries, lithium-ion capacitors, and electric double-layer capacitors are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, in recent years, improvements in battery members such as electrodes have been studied for the purpose of further improving the performance of electrochemical devices.

Here, an electrode used in an electrochemical device usually includes a current collector and an electrode mixture layer formed on the current collector. Then, the electrode mixture layer is formed by coating an electrode slurry containing, for example, an electrode active material, a conductive material, a binder composition containing a binder, etc. on a current collector, and applying the electrode slurry. formed by drying

Therefore, in recent years, studies have been made to improve the performance of electrochemical devices by improving polymer components such as binders.
For example, Patent Document 1 proposes to use a predetermined copolymer containing units derived from (meth)acrylonitrile and units derived from a conjugated diene monomer. According to Patent Document 1, the above copolymer functions as a dispersant for dispersing conductive materials such as carbon nanotubes (hereinafter sometimes abbreviated as "CNT"). Therefore, in Patent Document 1, in order to sufficiently disperse the conductive material, the conductive material and the copolymer are premixed to form a conductive material dispersion, and the obtained conductive material dispersion, the electrode active material, etc. are combined to form an electrode. methods of preparing slurries for liquids have been used.

JP 2020-187866 A

However, the above conventional technology has a problem that the internal resistance of the electrochemical element increases when charging and discharging are repeated. That is, the above-described conventional techniques have room for improvement in terms of suppressing the increase in internal resistance after cycling of the electrochemical device.

Therefore, the present invention provides a binder composition for an electrochemical element capable of forming an electrode capable of suppressing an increase in internal resistance after cycling of the electrochemical element, a conductive material dispersion for an electrochemical element, and a slurry for an electrode of an electrochemical element. for the purpose of providing
Another object of the present invention is to provide an electrochemical device in which an increase in internal resistance after cycling is suppressed.

The inventor of the present invention conducted intensive studies with the aim of solving the above problems. Then, the inventors of the present invention contain a predetermined polymer, N-methyl-2-pyrrolidone (hereinafter sometimes abbreviated as "NMP") as an organic solvent, and a predetermined nitrogen compound, The inventors have found that by using a binder composition that satisfies a predetermined relationship between coalescence and a nitrogen compound, it is possible to produce an electrode capable of suppressing an increase in internal resistance after cycling of an electrochemical device, and have completed the present invention. .

That is, an object of the present invention is to advantageously solve the above-mentioned problems. According to the present invention, the following [1] to [6] binder compositions for electrochemical elements, the following [7] to The conductive material dispersion for electrochemical elements of [10], the slurry for electrochemical element electrodes of [11] to [12] below, the electrode for electrochemical elements of [13] below, and the electrochemical element of [14] below. provided.
[1] A binder composition for an electrochemical device containing a polymer X, N-methyl-2-pyrrolidone, and a nitrogen compound other than the N-methyl-2-pyrrolidone, wherein the polymer X contains a nitrile group and at least one of an aliphatic conjugated diene monomer unit and an alkylene structural unit, the nitrogen compound has a molecular weight of 1,000 or less, and the Hansen solubility parameter (HSP _N ) and the Hansen solubility parameter (HSP _x ) of the polymer X, the HSP distance (R _A ) being 10.0 MPa ^1/2 or less.
According to an electrode produced using a binder composition containing both the above-described polymer X and the above-described nitrogen compound in NMP, and in which the HSP distance (R _A ) between the nitrogen compound and the polymer X is the above-described value or less , an increase in internal resistance after cycling of the electrochemical device can be suppressed.

Here, in the present invention, "monomer unit" means "a structural unit (repeating unit) derived from the monomer and contained in the polymer obtained by using the monomer". In the present invention, the term "alkylene structural unit" means "a structural unit composed only of an alkylene structure represented by the general formula -C _n H _2n - [wherein n is an integer of 2 or more]". Then, the ratio of each structural unit contained in the polymer can be measured using nuclear magnetic resonance (NMR) methods such as ¹ H-NMR and ¹³ C-NMR.
In the present invention, "Hansen solubility parameter of nitrogen compound (HSP _N )" is composed of polar term δ _p1 , dispersion term δ _d1 and hydrogen bonding term δ _h1 , and "Hansen solubility parameter of polymer X (HSP _X )” consists of a polar term δ _p2 , a dispersion term δ _d2 and a hydrogen bonding term δ _h2 .
Here, in the present invention, “δ _p1 ”, “δ _d1 ” and “δ _h1 ”, and “δ _p2 ”, “δ _d2 ” and “δ _h2 ” are specified using the method described in the examples. can do.
In the present invention, the "HSP distance (R _A )" is defined by the following formula (A):
HSP distance (R _A )={(δ _p1 −δ _p2 ) ² +4×(δ _d1 −δ _d2 ) ² +(δ _h1 −δ _h2 ) ² } ^1/2 (A)
can be calculated using

[2] The binder composition for electrochemical elements according to [1] above, wherein the polymer X has a weight average molecular weight of 300,000 or less.
If the weight average molecular weight of the polymer X is equal to or less than the value described above, the conductive material such as CNTs is well dispersed in the conductive material dispersion prepared using the binder composition (that is, the conductive material dispersion dispersibility can be improved), and an increase in internal resistance after cycling of the electrochemical device can be further suppressed.
In the present invention, the "weight average molecular weight" of the polymer can be measured using the method described in Examples.

[3] The binder composition for an electrochemical element according to [1] or [2] above, wherein the polymer X has a sulfur content of 500 ppm by mass or more.
If the amount of sulfur contained in the polymer X is at least the value described above, it is possible to improve the dispersibility of the conductive material dispersion and further suppress the increase in the internal resistance after cycling of the electrochemical device.
In the present invention, the "sulfur content" of the polymer can be measured using the method described in Examples.

[4] The binder composition for an electrochemical element according to any one of [1] to [3] above, wherein the polar term δ _p1 in the Hansen solubility parameter (HSP _N ) of the nitrogen compound is 14.0 MPa ^1/2 or less. thing.
If the polar term δ _p1 in the Hansen solubility parameter (HSP _N ) of the nitrogen compound is equal to or less than the above value, the dispersibility of the conductive material and the temporal stability of the electrode slurry prepared using the binder composition are improved. At the same time, the increase in internal resistance after cycling of the electrochemical device can be further suppressed.

[5] The binder composition for electrochemical elements according to any one of [1] to [4] above, wherein the nitrogen compound has a cyclic amidine structure.
A nitrogen compound having a cyclic amidine structure has an excellent effect of reducing the viscosity of a binder composition (viscosity reduction effect). An increase in internal resistance after cycling of the electrochemical device can be further suppressed.

[6] Any one of [1] to [5] above, wherein the mass ratio of the nitrogen compound in the total mass of the polymer X and the nitrogen compound is 0.1% by mass or more and 40% by mass or less. The binder composition for electrochemical elements according to .
If the mass of the nitrogen compound in the sum of the mass of the polymer X and the mass of the nitrogen compound is within the range described above, the dispersibility of the conductive material dispersion and the stability of the electrode slurry over time can be improved, and electrochemical It is possible to further suppress an increase in the internal resistance after the device is cycled.

[7] A conductive material dispersion for electrochemical elements, comprising the binder composition for electrochemical elements according to any one of [1] to [6] above and a fibrous conductive material. According to the electrode produced using the conductive material dispersion containing any of the binder compositions described above and the fibrous conductive material, it is possible to suppress an increase in internal resistance after cycling of the electrochemical device.
In the present invention, "fibrous conductive material" means a conductive material having an aspect ratio of 10 or more as measured using a transmission electron microscope (TEM).

[8] The conductive material dispersion for an electrochemical device according to [7] above, wherein the fibrous conductive material is a bundle type.
By using the bundle-type fibrous conductive material, it is possible to further improve the dispersibility of the conductive material dispersion and further suppress the increase in the internal resistance of the electrochemical device after cycling.
In the present invention, the term “bundle type” refers to a bundle-like or rope-like secondary shape in which a plurality of fibrous conductive materials are arranged or aligned in a certain direction.

[9] The conductive material dispersion for an electrochemical element according to [7] or [8] above, wherein the fibrous conductive material has a surface acidity of 0.01 mmol/g or more and 0.20 mmol/g or less.
If the surface acidity of the fibrous conductive material is within the range described above, the increase in internal resistance after cycling of the electrochemical element can be further improved while improving the dispersibility of the conductive material dispersion and the temporal stability of the electrode slurry. can be suppressed.
In the present invention, the "surface acidity" and the later-described "surface base content" of the fibrous conductive material can be measured using the methods described in Examples.

[10] The fibrous conductive material is a fibrous carbon material, and the ratio of the D band peak intensity to the G band peak intensity in the Raman spectrum of the fibrous carbon material is 2.0 or less [7] to [ 9].
Regarding the fibrous carbon material as the fibrous conductive material, the ratio of the D band peak intensity to the G band peak intensity in the Raman spectrum (hereinafter sometimes abbreviated as "D/G ratio") is the above value or less. Thus, it is possible to further suppress an increase in internal resistance after cycling of the electrochemical device while improving the dispersibility of the conductive material dispersion and the temporal stability of the electrode slurry.
In the present invention, the "ratio of the D band peak intensity to the G band peak intensity in the Raman spectrum" of the fibrous carbon material can be measured using the method described in Examples.

[11] A slurry for an electrochemical element electrode, comprising the conductive material dispersion for an electrochemical element according to any one of [7] to [10] above and an electrode active material.
According to the electrode produced using the electrode slurry containing any of the conductive material dispersions described above and the electrode active material, it is possible to suppress an increase in internal resistance after cycling of the electrochemical device.

[12] The slurry for an electrochemical element electrode according to [11] above, which further contains a binder other than the polymer X.
If the electrode slurry contains a binder other than the polymer X (hereinafter sometimes abbreviated as "other binder") in addition to the conductive material dispersion and the electrode active material described above, the electrode slurry The electrode mixture layer obtained using the slurry can be firmly adhered to the current collector (that is, the peel strength of the electrode can be improved), and the increase in internal resistance after cycling of the electrochemical device can be further suppressed. .

[13] An electrode for an electrochemical device, comprising an electrode mixture layer formed using the slurry for an electrochemical device electrode according to [11] or [12] above.
According to the electrode provided with the electrode mixture layer obtained using any of the electrode slurries described above, it is possible to suppress an increase in internal resistance after cycling of the electrochemical device.

[14] An electrochemical device comprising the electrode for an electrochemical device according to [13] above.
An electrochemical device having the electrodes described above has a suppressed increase in internal resistance after cycles.

According to the present invention, a binder composition for an electrochemical element capable of forming an electrode capable of suppressing an increase in internal resistance after cycling of the electrochemical element, a conductive material dispersion for an electrochemical element, and a slurry for an electrochemical element electrode. can be provided.
Moreover, according to the present invention, it is possible to provide an electrochemical device in which an increase in internal resistance after cycles is suppressed.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail.
Here, the binder composition for electrochemical elements of the present invention can be used when preparing slurry for electrochemical element electrodes. Further, the binder composition for electrochemical elements of the present invention is mixed with a fibrous conductive material such as CNT, and the conductive material for electrochemical elements of the present invention containing the binder composition for electrochemical elements and the fibrous conductive material. After making it into a dispersion liquid, it can be used for preparation of the slurry for electrochemical element electrodes. The slurry for an electrochemical element electrode of the present invention prepared using the conductive material dispersion for an electrochemical element can be used when forming an electrode for an electrochemical element such as a lithium ion secondary battery. Furthermore, the electrochemical device of the present invention is characterized by comprising the electrode for an electrochemical device of the present invention formed using the slurry for an electrochemical device electrode.

(Binder composition for electrochemical device)
The binder composition of the present invention contains polymer X, nitrogen compound, and NMP, and optionally further contains components other than polymer X, nitrogen compound, and NMP (other components).
Here, in the binder composition of the present invention,
the polymer X comprises a nitrile group-containing monomer unit and at least one of an aliphatic conjugated diene monomer unit and an alkylene structural unit;
The nitrogen compound has a molecular weight of 1,000 or less, and
The HSP distance (R _A ) between the Hansen solubility parameter (HSP _N ) of the nitrogen compound and the Hansen solubility parameter (HSP _X ) of the polymer X is 10.0 MPa ^1/2 or less;
is required.

When the binder composition of the present invention containing the polymer X and the nitrogen compound described above and having an HSP distance (R _A ) of the above value or less is used, an increase in the internal resistance of the electrochemical device after cycling can be suppressed. can be fabricated.

<Polymer X>
The polymer X is a component capable of functioning as a binder that holds the electrode active material and the like from the current collector without detaching from the electrode mixture layer formed using the binder composition. The polymer X can also function as a dispersant capable of dispersing the fibrous conductive material in the conductive material dispersion liquid prepared using the binder composition.

<<Composition>>
Here, the polymer X contains at least a nitrile group-containing monomer unit and an aliphatic conjugated diene monomer unit and/or an alkylene structural unit, as described above. The polymer X may contain structural units (other structural units) other than the nitrile group-containing monomer units, the aliphatic conjugated diene monomer units, and the alkylene structural units.

[Nitrile group-containing monomer unit]
Nitrile group-containing monomers capable of forming nitrile group-containing monomer units include α,β-ethylenically unsaturated nitrile monomers. Specifically, the α,β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group. Examples include acrylonitrile; α-chloroacrylonitrile; α-halogenoacrylonitrile such as α-bromoacrylonitrile; α-alkylacrylonitrile such as methacrylonitrile and α-ethylacrylonitrile; Incidentally, the nitrile group-containing monomer may be used singly, or two or more of them may be used in combination at an arbitrary ratio. And among these, acrylonitrile is preferable.

The content of the nitrile group-containing monomer unit in the polymer X is preferably 10% by mass or more, more preferably 20% by mass or more, based on 100% by mass of the total structural units in the polymer X. It is preferably 30% by mass or more, particularly preferably 35% by mass or more, preferably 50% by mass or less, and more preferably 40% by mass or less. When the content of the nitrile group-containing monomer unit in the polymer X is 10% by mass or more, the stability over time of the electrode slurry can be improved. An increase in internal resistance after cycles can be further suppressed.

[Aliphatic conjugated diene monomer unit and alkylene structural unit]
Aliphatic conjugated diene monomers capable of forming aliphatic conjugated diene monomer units include, for example, 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1, Examples include conjugated diene compounds having 4 or more carbon atoms such as 3-butadiene and 1,3-pentadiene. One of these may be used alone, or two or more of them may be used in combination at any ratio. Among these, 1,3-butadiene is preferred.

The alkylene structural unit may be linear or branched, but from the viewpoint of improving the dispersibility of the conductive material dispersion and further suppressing the increase in internal resistance after cycling of the electrochemical device. is preferably a linear alkylene structural unit, that is, a linear alkylene structural unit. Also, the number of carbon atoms in the alkylene structural unit is preferably 4 or more (that is, n in the general formula —C _n H _2n — is an integer of 4 or more).

Here, the method of introducing the alkylene structural unit into the polymer X is not particularly limited, but for example the following methods (1) and (2):
(1) A method of preparing a polymer from a monomer composition containing an aliphatic conjugated diene monomer and hydrogenating the polymer to convert the aliphatic conjugated diene monomer unit into an alkylene structural unit. (2) A method of preparing a polymer from a monomer composition containing a 1-olefin monomer.
Among these, the method (1) is preferable because the production of the polymer X is easy.

As the aliphatic conjugated diene monomer that can be used in the method (1), those described above as "aliphatic conjugated diene monomer capable of forming an aliphatic conjugated diene monomer unit" can be used. Among these, 1,3-butadiene is preferred. That is, the alkylene structural unit is preferably a structural unit obtained by hydrogenating an aliphatic conjugated diene monomer unit (aliphatic conjugated diene hydride unit), and hydrogenating a 1,3-butadiene monomer unit. Structural units (1,3-butadiene hydride units) obtained by
Examples of 1-olefin monomers include ethylene, propylene and 1-butene.
When forming the alkylene structural unit, each of the aliphatic conjugated diene monomer and the 1-olefin monomer may be used alone, or two or more may be used in combination at any ratio. good.

Here, the polymer X may contain at least one of an aliphatic conjugated diene monomer unit and an alkylene structural unit as described above. may contain a structural unit, may contain an aliphatic conjugated diene monomer unit without containing an alkylene structural unit, or may contain both an aliphatic conjugated diene monomer unit and an alkylene structural unit . However, from the viewpoint of further suppressing the increase in internal resistance after cycling of the electrochemical device while improving the dispersibility of the conductive material dispersion, the polymer X contains an aliphatic conjugated diene monomer unit and an alkylene structural unit. Among them, it preferably contains at least an alkylene structural unit, and more preferably contains both an aliphatic conjugated diene monomer unit and an alkylene structural unit.

Then, the total content of the aliphatic conjugated diene monomer units and the alkylene structural units in the polymer X is preferably 30% by mass or more, with the total structural units in the polymer X being 100% by mass. It is more preferably 60% by mass or more, particularly preferably 65% by mass or more, preferably 80% by mass or less, and preferably 75% by mass or less. More preferably, it is 70% by mass or less. If the sum of the content of the aliphatic conjugated diene monomer unit and the content of the alkylene structural unit in the polymer X is 30% by mass or more, the increase in internal resistance after cycling of the electrochemical device can be further suppressed. If it is 80% by mass or less, the stability of the electrode slurry over time can be improved.

[Other structural units]
Examples of other structural units include, but are not particularly limited to, (meth)acrylic acid ester monomer units, aromatic-containing monomer units, and hydrophilic group-containing monomer units. The polymer X may contain one type of other repeating unit, or may contain two or more types of other repeating units.
In addition, in this invention, "(meth)acryl" means acryl and/or methacryl.

(Meth)acrylic acid ester monomers capable of forming (meth)acrylic acid ester monomer units include, for example, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl Alkyl acrylates such as acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate Ester; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl Methacrylic acid alkyl esters such as methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate; The (meth)acrylic acid ester monomers may be used singly or in combination of two or more at any ratio.

Examples of aromatic-containing monomers capable of forming aromatic-containing monomer units include aromatic compounds such as styrene, α-methylstyrene, pt-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene and vinylnaphthalene. group monovinyl monomers. The aromatic-containing monomers may be used singly or in combination of two or more at any ratio.

Examples of hydrophilic group-containing monomer units include carboxylic acid group-containing monomer units, sulfonic acid group-containing monomer units, phosphoric acid group-containing monomer units, and hydroxyl group-containing monomer units. In other words, the hydrophilic group-containing monomer capable of forming the hydrophilic group-containing monomer unit includes a carboxylic acid group-containing monomer, a sulfonic acid group-containing monomer, a phosphoric acid group-containing monomer, and Examples include hydroxyl group-containing monomers. The hydrophilic group-containing monomers may be used singly or in combination of two or more at any ratio.

Carboxylic acid group-containing monomers include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, their derivatives, and the like.
Monocarboxylic acids include acrylic acid, methacrylic acid, crotonic acid and the like.
Monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, β-diaminoacrylic acid, and the like. mentioned.
Dicarboxylic acids include maleic acid, fumaric acid, itaconic acid, and the like.
Dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, methyl allyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, and dodecyl maleate. , octadecyl maleate, and fluoroalkyl maleate.
Acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.
As the monomer having a carboxylic acid group, an acid anhydride that produces a carboxyl group by hydrolysis can also be used.
Others, monoethyl maleate, diethyl maleate, monobutyl maleate, dibutyl maleate, monoethyl fumarate, diethyl fumarate, monobutyl fumarate, dibutyl fumarate, monocyclohexyl fumarate, dicyclohexyl fumarate, monoethyl itaconate, diethyl itaconate Also included are monoesters and diesters of α,β-ethylenically unsaturated polycarboxylic acids such as , monobutyl itaconate, and dibutyl itaconate.

Examples of sulfonic acid group-containing monomers include vinylsulfonic acid, methylvinylsulfonic acid, (meth)allylsulfonic acid, styrenesulfonic acid, ethyl (meth)acrylate-2-sulfonate, and 2-acrylamido-2-methylpropane. sulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and the like.
In the present invention, "(meth)allyl" means allyl and/or methallyl.

Phosphate group-containing monomers include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl phosphate-(meth)acryloyloxyethyl phosphate.
In the present invention, "(meth)acryloyl" means acryloyl and/or methacryloyl.

Examples of hydroxyl group-containing monomers include (meth)allyl alcohol, 3-buten-1-ol, ethylenically unsaturated alcohols such as 5-hexene-1-ol; 2-hydroxyethyl acrylate, 2-acrylate Ethylenically unsaturated compounds such as hydroxypropyl, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, and di-2-hydroxypropyl itaconate. Alkanol esters of saturated carboxylic acids; general formula: CH ₂ ═CR ^A —COO—(C _k H _2k O) _m —H (wherein m is an integer of 2 to 9, k is an integer of 2 to 4, R ^A represents hydrogen or a methyl group) esters of polyalkylene glycol and (meth)acrylic acid; 2-hydroxyethyl-2'-(meth)acryloyloxyphthalate, 2-hydroxyethyl-2'- Mono(meth)acrylic acid esters of dihydroxy esters of dicarboxylic acids such as (meth)acryloyloxysuccinate; vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; (meth)allyl-2-hydroxyethyl ether , (meth) allyl-2-hydroxypropyl ether, (meth) allyl-3-hydroxypropyl ether, (meth) allyl-2-hydroxybutyl ether, (meth) allyl-3-hydroxybutyl ether, (meth) allyl-4- Alkylene glycol mono(meth)allyl ethers such as hydroxybutyl ether and (meth)allyl-6-hydroxyhexyl ether; Polyoxyalkylene glycol mono(meth)allyl ethers such as diethylene glycol mono(meth)allyl ether and dipropylene glycol mono(meth)allyl ether (Meth)allyl ethers; (poly) such as glycerin mono(meth)allyl ether, (meth)allyl-2-chloro-3-hydroxypropyl ether, (meth)allyl-2-hydroxy-3-chloropropyl ether Halogen- and hydroxy-substituted mono (meth) allyl ethers of alkylene glycol; mono (meth) allyl ethers of polyhydric phenols such as eugenol and isoeugenol and their halogen substitutions; (meth) allyl-2-hydroxyethyl thioether, ( Alkylene glycols such as meth)allyl-2-hydroxypropylthioether (meth) allyl thioethers of; and the like.

The content of other structural units in polymer X is preferably 30% by mass or less, more preferably 10% by mass or less, based on 100% by mass of all structural units in polymer X. . If the content ratio of other structural units is 30% by mass or less, the effect of reducing the viscosity of the binder composition is enhanced in relation to the nitrogen compound described later, and the initial dispersion viscosity when the conductive material dispersion is prepared is reduced. obtain. That is, it is possible to improve the dispersibility of the conductive material dispersion. Further, when the content of other structural units is 30% by mass or less, the stability of the electrode slurry over time can be improved. Needless to say, the polymer X may not contain other structural units. That is, the content of other structural units in polymer X may be 0% by mass.

<<Properties>>
Here, the polymer X is not particularly limited, but preferably has the following properties.

[Sulfur content]
Polymer X preferably has a sulfur content of 500 mass ppm or more, more preferably 1,000 mass ppm or more, still more preferably 3,000 mass ppm or more, and 4,000 mass ppm. It is particularly preferably 20,000 mass ppm or less, more preferably 10,000 mass ppm or less, even more preferably 8,000 mass ppm or less, 6,000 mass ppm ppm or less is particularly preferred. When the sulfur content of the polymer X is 500 ppm by mass or more, the structure viscosity of the conductive material dispersion is suppressed and the initial dispersion TI value is reduced, thereby improving the dispersibility of the conductive material dispersion. can be made In addition, it is presumed that the polymer X contains a sulfur atom in the molecule, so that the oxidation resistance of the polymer X increases. It is possible to further suppress an increase in internal resistance after cycling of the electrochemical device. On the other hand, if the amount of sulfur contained in the polymer X is 20,000 mass ppm or less, the occurrence of structural viscosity of the conductive material dispersion is suppressed, the initial dispersion TI value is lowered, etc., and the conductive material dispersion is dispersed. can improve sexuality. In addition, the stability of the electrode slurry over time can be improved.
The amount of sulfur contained in the polymer X can be controlled, for example, based on the amount of a compound having a sulfur-containing group such as a mercapto group (molecular weight modifier) added during polymerization.

[Iodine value]
The polymer X preferably has an iodine value of 100 mg/100 mg or less, more preferably 80 mg/100 mg or less, still more preferably 70 mg/100 mg or less, and particularly preferably 50 mg/100 mg or less. . If the iodine value of the polymer X is 100 mg/100 mg or less, the dispersibility of the conductive material dispersion and the stability of the electrode slurry over time are improved, while the increase in internal resistance after cycling of the electrochemical device is further suppressed. be able to. Although the lower limit of the iodine value of the polymer X is not particularly limited, it can be, for example, 0.1 mg/100 mg or more, 1 mg/100 mg or more, or 5 mg/100 mg or more.
In addition, in this invention, an "iodine number" can be measured using the method as described in an Example.

[Weight average molecular weight]
Polymer X preferably has a weight average molecular weight of more than 1,000, more preferably 5,000 or more, even more preferably 10,000 or more, and more preferably 20,000 or more. It is more preferably 25,000 or more, particularly preferably 300,000 or less, preferably 250,000 or less, more preferably 100,000 or less, and 70,000 or less. more preferably 50,000 or less. If the weight-average molecular weight of the polymer X is more than 1,000, the effect of reducing the viscosity of the binder composition is increased in relation to the nitrogen compound described later, and the dispersibility of the conductive material dispersion can be improved. . On the other hand, if the weight average molecular weight of the polymer X is 300,000 or less, the dispersibility of the conductive material dispersion can be improved by reducing the initial dispersion TI value. In addition, it is possible to further suppress an increase in internal resistance after cycling of the electrochemical device.

<<Preparation method>>
A method for preparing the polymer X is not particularly limited. Polymer X is produced, for example, by polymerizing a monomer composition containing the above-described monomers in an aqueous solvent and optionally hydrogenating (hydrogenating) the polymer. The content ratio of each monomer in the monomer composition can be determined according to the content ratio of each structural unit in the polymer X.
The polymerization mode is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method and an emulsion polymerization method can be used. As the polymerization reaction, addition polymerization such as ionic polymerization, radical polymerization, and living radical polymerization can be used. As the polymerization initiator, a known polymerization initiator such as a redox polymerization initiator containing an iron-based compound can be used.

Here, in the polymerization, the molecular weight (particularly the weight-average molecular weight) of the polymer X obtained can be adjusted by using a molecular weight modifier. Examples of such molecular weight modifiers include compounds having a sulfur-containing group such as a mercapto group. Compounds having a mercapto group as molecular weight modifiers include, for example, octylmercaptan, 2,2,4,6,6-pentamethyl-4-heptanethiol, 2,4,4,6,6-pentamethyl-2- Carbon such as heptanethiol, 2,3,4,6,6-pentamethyl-2-heptanethiol, 2,3,4,6,6-pentamethyl-3-heptanethiol, t-dodecylmercaptan, n-dodecylmercaptan, etc. Compounds having a mercapto group of numbers 8 to 12; Compounds having a mercapto group such as (2-mercaptoethyl) sulfide, methyl 3-mercaptopropionate, and 1-butanethiol can be mentioned.

Further, when the polymer X is produced by the method (1) above, a polymer to be hydrogenated (that is, a polymer containing a nitrile group-containing monomer unit and an aliphatic conjugated diene monomer unit) As the polymerization method of (1), radical polymerization using a redox polymerization initiator containing an iron-based compound can be used. Here, the redox polymerization initiator containing an iron-based compound is not particularly limited. For example, cumene hydroperoxide as a polymerization initiator and ferrous sulfate and/or ethylenediaminetetraacetic acid as an iron-based compound Combinations with monosodium iron can be used.
In addition, when the polymer X is produced by the above method (1), after emulsion polymerization, it is coagulated with a coagulant and recovered, and the recovered polymer is recovered (optionally after carrying out the “metathesis reaction” described later). It can also be hydrogenated.
Further, hydrogenation can be carried out using known hydrogenation methods such as oil layer hydrogenation or water layer hydrogenation. As the catalyst used for hydrogenation, any known selective hydrogenation catalyst can be used without limitation, and a palladium-based catalyst or a rhodium-based catalyst can be used. Two or more of these may be used in combination.

Hydrogenation of the polymer may be carried out using the method described in Japanese Patent No. 4509792, for example. Specifically, hydrogenation of the polymer may be carried out after conducting a metathesis reaction of the polymer in the presence of a catalyst and a co-(co-)olefin.
Here, a known ruthenium-based catalyst can be used as a metathesis reaction catalyst. Among them, metathesis catalysts include bis(tricyclohexylphosphine)benzylidene ruthenium dichloride, 1,3-bis(2,4,6-trimethylphenyl)-2-(imidazolidinylidene) (dichlorophenylmethylene) (tricyclohexyl) Grubbs catalysts such as xylphosphine)ruthenium are preferably used. As coolefins, olefins having 2 to 16 carbon atoms such as ethylene, isobutane and 1-hexane can be used. As the hydrogenation catalyst for hydrogenation after the metathesis reaction, a known homogeneous hydrogenation catalyst such as Wilkinson's catalyst ((PPh ₃ ) ₃ RhCl) can be used.

<Nitrogen compound>
A nitrogen compound is an organic compound (excluding NMP) containing a nitrogen atom.

<<HSP distance (R _A )>>
Here, in the binder composition of the present invention, it is necessary that the HSP distance (R _A ) between the nitrogen compound and the polymer X is 10.0 MPa ^1/2 or less. Since the HSP distance (R _A ) is 10.0 MPa ^1/2 or less, the affinity between the nitrogen compound and the polymer X is high. Therefore, it is presumed that the use of the nitrogen compound in the preparation of the binder composition weakens the interaction between the polymer chains constituting the polymer X, but the use of the nitrogen compound reduces the viscosity of the binder composition. (viscosity reduction effect). By preparing a conductive material dispersion and/or electrode slurry using a binder composition with sufficiently reduced viscosity, it is possible to form an electrode mixture layer in which components such as fibrous conductive materials are well dispersed. becomes. As a result, an increase in internal resistance after cycling of the electrochemical device can be suppressed.
Then, from the viewpoint of better exhibiting the above effects, the HSP distance (R _A ) is preferably 8.0 MPa ^1/2 or less, more preferably 6.0 MPa ^1/2 or less. 0.6 MPa ^1/2 or less is more preferable. The lower limit of the HSP distance (R _A ) is not particularly limited, but is, for example, 0.1 MPa ^1/2 or more.

Here, the HSP distance (R _A ) constitutes the Hansen solubility parameter of the nitrogen compound (HSP _N ) and the Hansen solubility parameter of the polymer X (HSP _X ), respectively, as can be seen from the above formula (A). can be adjusted by controlling the polar term, the dispersion term, and the hydrogen bonding term.
The Hansen solubility parameter (HSP _N ) of the nitrogen compound can be changed by selecting the type of nitrogen compound. Regarding the Hansen solubility parameter (HSP _X ) of polymer X, the type and proportion of the monomers used in the preparation of polymer X, and the weight average molecular weight, iodine value, and sulfur content of polymer X are changed. can be controlled by

<<Polarity term δ _p1 >>
In the Hansen solubility parameter (HSP _N ) of the nitrogen compound, the polar term δ _p1 is preferably 14.0 or more and MPa ^1/2 or less, more preferably 11.0 MPa ^1/2 or less. If the polar term δ _p1 is 14.0 MPa ^1/2 or less, the nitrogen compound can sufficiently exhibit the viscosity reducing effect described above without excessively increasing the acid dissociation constant of the nitrogen compound. Therefore, it is possible to further suppress an increase in internal resistance after cycling of the electrochemical element while improving the dispersibility of the conductive material dispersion and the temporal stability of the electrode slurry.
Although the lower limit of the polarity term δ _p1 is not particularly limited, it is, for example, 5.0 MPa ^1/2 or more.

<<molecular weight>>
Here, the nitrogen compound must have a molecular weight of 1,000 or less, preferably 50 or more, more preferably 60 or more, even more preferably 70 or more, and 80 or more. It is particularly preferably 600 or less, more preferably 300 or less, even more preferably 200 or less, and particularly preferably 130 or less. If the molecular weight of the nitrogen compound exceeds 1,000, a sufficient viscosity reduction effect cannot be obtained, and an increase in internal resistance after cycling of the electrochemical device cannot be suppressed. In addition, the stability of the electrode slurry over time is lowered. On the other hand, if the molecular weight of the nitrogen compound is 50 or more, the viscosity reduction effect described above can be sufficiently obtained, and the increase in internal resistance after cycling of the electrochemical element can be further improved while improving the dispersibility of the conductive material dispersion. can be suppressed.

<<Structure>>
Also, the nitrogen compound preferably has a cyclic amidine structure. A nitrogen compound having a cyclic amidine structure is particularly effective in reducing viscosity, and by using a nitrogen compound having a cyclic amidine structure, the dispersibility of the conductive material dispersion is improved by reducing the initial dispersion viscosity and the initial dispersion TI value. In addition, the increase in internal resistance of the electrochemical device after cycling can be further suppressed.
In addition, the nitrogen compound preferably does not have an aromatic ring such as a benzene ring from the viewpoint of improving the dispersibility of the conductive material dispersion and further suppressing an increase in internal resistance after cycling of the electrochemical device.

<<Specific example>>
Here, preferred specific examples of nitrogen compounds include 2-methyl-2-imidazoline, 2-propyl-2-imidazoline, diazabicycloundecene (DBU), diazabicyclononene (DBN), 1,5,7 -triazabicyclo[4.4.0]dec-5-ene (TBD). The nitrogen compounds may be used singly, or two or more of them may be used in combination at any ratio.
As the nitrogen compound, 2-methyl-2- Imidazoline and DBU are preferred, and 2-methyl-2-imidazoline is more preferred.

<<mixing ratio>>
In the binder composition of the present invention, the mixing ratio of the polymer X and the nitrogen compound is not particularly limited. It is preferably at least 1% by mass, more preferably at least 1% by mass, more preferably at least 3% by mass, even more preferably at least 5% by mass, and preferably at most 40% by mass, It is more preferably 30% by mass or less, and even more preferably 20% by mass or less. If the ratio of the nitrogen compound in the total mass of the polymer X and the nitrogen compound is 0.1% by mass or more, the viscosity reduction effect can be sufficiently exhibited, and if it is 40% by mass or less, the electrode slurry can improve the stability over time. Then, if the ratio of the nitrogen compound in the total mass of the polymer X and the nitrogen compound is 0.1% by mass or more and 40% by mass or less, the electrochemical device can be cycled while improving the dispersibility of the conductive material dispersion. Later increase in internal resistance can be further suppressed.

<Other ingredients>
Other components that the binder composition of the present invention may contain in addition to the polymer X, NMP, and nitrogen compound are not particularly limited. Examples thereof include binders other than the polymer X described later, reinforcing materials, leveling agents, viscosity modifiers, and electrolytic solution additives. These are not particularly limited as long as they do not affect the battery reaction, and known ones such as those described in International Publication No. 2012/115096 can be used. Moreover, the binder composition of the present invention may contain an organic solvent that is neither NMP nor a nitrogen compound.
In addition, these other components may be used individually by 1 type, and may be used in combination of 2 or more types by arbitrary ratios.

<Method for preparing binder composition>
The method for preparing the binder composition of the present invention is not particularly limited, and it can be obtained by mixing the above-described components using a known mixing device such as a disper.

(Conductive material dispersion)
The conductive material dispersion of the present invention is a composition containing a fibrous conductive material and the binder composition described above. That is, the conductive material dispersion of the present invention contains the fibrous conductive material, the polymer X described above, NMP, and the nitrogen compound described above, and optionally a conductive material other than the fibrous conductive material (other conductive material) and/or other components. Here, in the conductive material dispersion of the present invention, as in the binder composition of the present invention described above, the HSP distance between the Hansen solubility parameter (HSP _N ) of the nitrogen compound and the Hansen solubility parameter (HSP _X ) of the polymer X (R _A ) is 10.0 MPa ^1/2 or less.
Since the conductive material dispersion of the present invention contains the binder composition of the present invention, the use of the conductive material dispersion of the present invention provides an electrode capable of suppressing an increase in internal resistance after cycling of an electrochemical device. can be made.
The conductive material dispersion of the present invention is an intermediate product for preparing the electrode slurry of the present invention, which will be described later, and usually does not contain an electrode active material. In addition, the polymer X and the nitrogen compound contained in the conductive material dispersion of the present invention are derived from the binder composition of the present invention, and their preferred abundance ratios are the same as those of the binder composition of the present invention. is.

<Fibrous conductive material>
Examples of fibrous conductive materials include fibrous carbon materials such as carbon nanotubes (single-walled CNTs, multi-walled CNTs), carbon nanohorns, carbon nanofibers, and milled carbon fibers. The fibrous conductive material may be used singly or in combination of two or more at any ratio. Among these, carbon nanotubes and carbon nanofibers are preferred, and carbon nanotubes are more preferred, from the viewpoint of further suppressing increases in internal resistance after cycling of the electrochemical device.
Moreover, it is preferable that the fibrous conductive material is a bundle type. By using the bundle-type fibrous conductive material, it is possible to improve the dispersibility of the conductive material dispersion and further suppress the increase in the internal resistance after cycling of the electrochemical device.

<<HSP distance (R _B )>>
In the conductive material dispersion of the present invention, the HSP distance (R _B ) between the Hansen solubility parameter (HSP _N ) of the nitrogen compound and the Hansen solubility parameter (HSP _F ) of the fibrous conductive material is 10.0 MPa ^1/2 or less. , more preferably 8.0 MPa ^1/2 or less, and even more preferably 6.0 MPa ^1/2 or less. If the HSP distance (R _B ) between the nitrogen compound and the fibrous conductive material is 10.0 MPa ^1/2 or less, the dispersibility of the conductive material dispersion is improved, and the internal resistance of the electrochemical element after cycling is reduced. The rise can be further suppressed. Although the reason for this is not clear, since the HSP distance (R _B ) is 10.0 MPa ^1/2 or less, the nitrogen compound that can interact well with the fibrous conductive material modifies the surface of the fibrous conductive material. This is presumed to be because the polymer X can be well adsorbed to the fibrous conductive material via the nitrogen compound (surface modification effect).
The lower limit of the HSP distance (R _B ) is not particularly limited, but is, for example, 0.1 MPa ^1/2 or more.

In the present invention, the "Hansen solubility parameter (HSP _F ) of the fibrous conductive material" is composed of the polar term δ _p3 , the dispersion term δ _d3 and the hydrogen bonding term δ _h3 .
Here, in the present invention, “δ _p3 ”, “δ _d3 ” and “δ _h3 ” can be specified using the method described in Examples.
In the present invention, the "HSP distance (R _B )" is defined by the following formula (B):
HSP distance (R _B )={(δ _p1 −δ _p3 ) ² +4×(δ _d1 −δ _d3 ) ² +(δ _h1 −δ _h3 ) ² } ^1/2 (B)
can be calculated using

As can be seen from the above formula (B), the HSP distance (R _B ) constitutes the Hansen solubility parameter (HSP _N ) of the nitrogen compound and the Hansen solubility parameter (HSP _X ) of the fibrous conductive material, respectively. can be adjusted by controlling the polar term, the dispersion term, and the hydrogen bonding term.
The Hansen solubility parameter (HSP _N ) of the nitrogen compound can be changed by selecting the type of nitrogen compound. Regarding the Hansen solubility parameter (HSP _F ) of the fibrous conductive material, the type of fibrous conductive material (material of the main component), the surface acid amount, the surface base amount, and the D/G ratio of the fibrous conductive material are changed. can be controlled by

<<D/G ratio>>
When a fibrous carbon material is used as the fibrous conductive material, the dispersibility of the conductive material dispersion is improved by reducing the TI value at the initial stage of dispersion, and the stability of the electrode slurry over time is improved. From the viewpoint of further suppressing an increase in internal resistance after cycling, the D/G ratio of the fibrous carbon material is preferably 2.0 or less, more preferably 1.5 or less.
Here, the D/G ratio is an index commonly used to evaluate the quality of carbon materials. Vibrational modes called G band (near 1600 cm ⁻¹ ) and D band (near 1350 cm ⁻¹ ) are observed in the Raman spectrum of a carbon material measured by a Raman spectrometer. The G band is a vibrational mode derived from the hexagonal lattice structure of graphite, and the D band is a vibrational mode derived from amorphous sites. Therefore, it can be said that a carbon material having a smaller peak intensity ratio (D/G ratio) between the D band and the G band has fewer amorphous portions, ie, fewer defective structures. According to the studies of the present inventors, the use of a fibrous carbon material with few defective structures improves the dispersibility of the conductive material dispersion liquid, such as by lowering the initial dispersion TI value, and furthermore, the conductive material dispersion It was clarified that the stability of the electrode slurry over time is improved and that the increase in internal resistance after cycling of the electrochemical device can be further suppressed due to the improvement in the dispersibility of the liquid.
The reason why the dispersibility of the conductive material dispersion is improved by using a fibrous carbon material with few defect structures is not clear, but the fibrous carbon material with few defect structures can satisfactorily improve the surface modification effect of the nitrogen compound described above. It is presumed that this is because the polymer X can be better adsorbed on the fibrous carbon material via the nitrogen compound.
Although the lower limit of the D/G ratio of the fibrous carbon material is not particularly limited, it is, for example, 0.01 or more. Also, the D/G ratio of the fibrous carbon material can be controlled by changing the conditions and the like when preparing the fibrous carbon material.

<<BET specific surface area>>
The fibrous conductive material preferably has a BET specific surface area of 100 m ² /g or more, more preferably 150 m ² /g or more, even more preferably 200 m ² /g or more, and 1,000 m ² . /g or less, more preferably 500 m ² /g or less, and even more preferably 400 m ² /g or less. If the BET specific surface area is within the range described above, it is possible to further suppress an increase in internal resistance after cycling of the electrochemical device while improving the dispersibility of the conductive material dispersion.
In the present invention, the "BET specific surface area" of the fibrous conductive material can be measured using the method described in Examples.

<< surface acidity >>
The fibrous conductive material preferably has a surface acidity of 0.01 mmol/g or more, preferably 0.20 mmol/g or less, and more preferably 0.15 mmol/g or less. If the surface acid amount of the fibrous conductive material is 0.01 mmol/g or more, it is presumed that the amount of the residual base component adhering to the surface of the fibrous conductive material is reduced, but the electrode slurry is stable over time. can enhance sexuality. On the other hand, if the surface acidity of the fibrous conductive material is 0.20 mmol/g or less, the amount of residual acid component adhering to the surface of the fibrous conductive material is reduced to suppress side reactions in the electrochemical device. It is presumed that this is because the increase in the internal resistance of the electrochemical device after cycling can be further suppressed.
In the present invention, the "surface base amount" and "surface acid amount" of the carbon nanotube can be measured using the methods described in Examples.

<<Surface acid amount/Surface base amount>>
In the fibrous conductive material, the ratio of the surface acid amount to the surface base amount (surface acid amount/surface base amount) is preferably 0.10 or more, more preferably 0.15 or more, and 0 It is more preferably 0.20 or more, preferably 2.5 or less, more preferably 2.0 or less, and even more preferably 1.5 or less. If the surface acid amount/surface base amount of the fibrous conductive material is 0.10 or more, it is presumed that the amount of the residual base component adhering to the surface of the fibrous conductive material is reduced. Stability over time can be improved. On the other hand, if the surface acid amount/surface base amount of the fibrous conductive material is 2.5 or less, the amount of the residual acid component adhering to the surface of the fibrous conductive material is reduced to prevent side reactions in the electrochemical device. It is presumed that this is because the increase in the internal resistance of the electrochemical device after cycling can be further suppressed.

<<Preparation method>>
A method for preparing the fibrous conductive material is not particularly limited. In the following, a method for preparing CNTs having a surface acid content and a surface acid content/surface base content within the preferred ranges described above will be described as an example.
CNTs whose surface acid content and surface acid content/surface base content are within the preferred ranges described above are obtained by subjecting the raw CNTs to an acid treatment (acid treatment step) and performing a base treatment on the acid-treated raw CNTs. It can be prepared through a process of treatment (base treatment process) and a process of washing the base-treated raw material CNTs (washing process).

[Acid treatment process]
In the acid treatment step, the raw CNTs are acid treated. Raw CNTs are not particularly limited, and can be appropriately selected from known CNTs according to desired properties of surface-treated CNTs (number of layers, D/G ratio, BET specific surface area, etc.).

Here, the acid treatment method is not particularly limited as long as the raw CNTs can be brought into contact with an acid, but a method of immersing the raw CNTs in an acid treatment solution (acid aqueous solution) is preferred.
The acid contained in the acid treatment liquid is not particularly limited, but examples thereof include nitric acid, sulfuric acid, and hydrochloric acid. These can be used individually by 1 type or in combination of 2 or more types. Among these, nitric acid and sulfuric acid are preferred.

The time for which the raw CNTs are immersed in the acid treatment solution (immersion time) is preferably 1 minute or longer, more preferably 10 minutes or longer, even more preferably 30 minutes or longer, and 50 minutes or longer. is particularly preferably 120 minutes or less, more preferably 100 minutes or less, and even more preferably 80 minutes or less. If the immersion time is 1 minute or more, the surface acid amount of the surface-treated CNT can be increased. Sufficient production efficiency is ensured.

The temperature (immersion temperature) at which the raw CNTs are immersed in the acid treatment solution is preferably 20°C or higher, more preferably 40°C or higher, preferably 80°C or lower, and 70°C. The following are more preferable. If the immersion temperature is within the range described above, the surface acidity of the resulting surface-treated CNT can be appropriately increased.

After the immersion, the acid-treated CNTs can be recovered by a known method such as filtration from the mixture of the CNTs that have undergone the acid treatment process (acid-treated CNTs) and the acid-treated solution. The collected acid-treated CNTs may be washed with water if necessary.

[Base treatment step]
In the base treatment step, the acid-treated CNTs obtained through the acid treatment step described above are subjected to base treatment.

Here, the method of base treatment is not particularly limited as long as the base can be brought into contact with the acid-treated CNTs, but a method of immersing the acid-treated CNTs in a base treatment solution (aqueous solution of base) is preferred.
The base contained in the base treatment liquid is not particularly limited, but examples thereof include lithium hydroxide, ammonium chloride, sodium bicarbonate and sodium hydroxide. These can be used individually by 1 type or in combination of 2 or more types. Among these, lithium hydroxide and ammonium chloride are preferred, and lithium hydroxide is more preferred.

The time for which the acid-treated CNTs are immersed in the base treatment solution (immersion time) is preferably 10 minutes or longer, more preferably 60 minutes or longer, even more preferably 80 minutes or longer, and 90 minutes or longer. It is particularly preferably 240 minutes or less, more preferably 200 minutes or less, and even more preferably 150 minutes or less. If the immersion time is 10 minutes or more, the surface base amount of the surface-treated CNT can be increased, and if it is 240 minutes or less, the surface base amount of the surface-treated CNT does not excessively increase. Sufficient production efficiency is ensured.

The temperature (immersion temperature) at which the acid-treated CNTs are immersed in the base treatment solution is preferably 10° C. or higher, more preferably 20° C. or higher, and preferably 40° C. or lower. °C or less is more preferable. If the immersion temperature is within the range described above, the surface base content of the resulting surface-treated CNT can be appropriately increased.

[Washing process]
In the washing step, raw material CNTs (acid-base-treated CNTs) obtained through the above-described acid treatment step and base treatment step are washed. By this washing, excess acid component and base component (especially base component) adhering to the surface of the acid-base treated CNT can be removed, and surface-treated CNT having predetermined properties can be obtained.

Although the method for washing the acid-base-treated CNT is not particularly limited, washing with water is preferable. For example, the acid-base-treated CNTs are recovered from a mixture of the acid-base-treated CNTs and the base-treated liquid by a known method such as filtration, and the acid-base-treated CNTs are washed with water. At this time, by measuring the electric conductivity of the water (washing water) used for washing the acid-base-treated CNTs, it is possible to estimate how much the acid component and the base component have been removed.
After the washing step described above, surface-treated CNTs can be obtained by removing water adhering to the surface by drying, if necessary.

The surface acid amount and surface base amount of the surface-treated CNT can be adjusted by changing the conditions of the acid treatment process, base treatment process, and washing process described above. For example, the amount of acid and base on the surface of the surface-treated CNT is adjusted by changing the types of acids and bases contained in the acid treatment process, the acid treatment liquid used in the base treatment process, and the base treatment liquid, respectively, and their concentrations. can do. In addition, by lengthening the immersion time in the acid treatment step, the surface acid amount of the surface-treated CNTs can be increased, and by lengthening the immersion time in the base treatment step, the surface base amount of the surface-treated CNTs can be increased. can. Furthermore, in the washing step, the amount of surface acid and the amount of surface base (particularly, the amount of surface base) can be adjusted by changing the degree of washing.

<Other conductive materials>
The other conductive material is not particularly limited as long as it is a conductive material having a shape other than fibrous (e.g., particulate, plate-like), carbon black (e.g., acetylene black, Ketjenblack (registered trademark), fur nest black, etc.), graphene, and the like. In addition, other conductive materials may be used singly, or two or more of them may be used in combination at an arbitrary ratio.

The mixing ratio of the fibrous conductive material and the optionally used other conductive material is not particularly limited, but from the viewpoint of sufficiently ensuring the dispersibility of the conductive material dispersion liquid, The ratio of the mass of the fibrous conductive material to the total mass of is preferably 50% by mass or more and 100% by mass or less.

<Binder composition>
As the binder composition, the binder composition of the present invention containing the polymer X described above, the nitrogen compound described above, NMP, and optionally other components is used.

Here, when the fibrous conductive material and the binder composition are mixed to obtain the conductive material dispersion, the quantitative ratio of the fibrous conductive material and the binder composition is not particularly limited. In the fibrous conductive material and the binder composition, for example, the obtained conductive material dispersion preferably contains 5 parts by mass or more and 40 parts by mass or less, more preferably 10 parts by mass of the polymer X per 100 parts by mass of the fibrous conductive material. It is sufficient to mix them in a quantity ratio such that they are contained in a proportion of 30 parts by mass or less.

<Method for preparing conductive material dispersion>
The method of preparing the conductive material dispersion is not particularly limited. The conductive material dispersion can be prepared by mixing the fibrous conductive material and the binder composition, for example, using a known mixing device. In preparing the conductive material dispersion, in addition to the fibrous conductive material and the binder composition, other conductive materials may be mixed together, or an organic solvent such as NMP may be further added.

(Slurry for electrochemical device electrodes)
The electrode slurry of the present invention is a composition containing an electrode active material and the conductive material dispersion described above. That is, the electrode slurry of the present invention contains at least the electrode active material, the fibrous conductive material described above, the polymer X described above, the nitrogen compound described above, and NMP. Here, the electrode slurry of the present invention preferably contains other binder from the viewpoint of further suppressing the increase in internal resistance after cycling of the electrochemical device while increasing the peel strength of the electrode.
Further, since the electrode slurry of the present invention contains the conductive material dispersion of the present invention, the electrode formed using the electrode slurry can prevent an increase in internal resistance after cycling of the electrochemical element. can be suppressed.
The fibrous conductive material, the polymer X and the nitrogen compound contained in the electrode slurry of the present invention are derived from the binder composition and the conductive material dispersion of the present invention. , the same as the binder composition and conductive material dispersion of the present invention.

<Electrode active material>
The electrode active material (positive electrode active material, negative electrode active material) to be blended in the electrode slurry is not particularly limited, and known electrode active materials can be used.

For example, positive electrode active materials used in lithium ion secondary batteries are not particularly limited, but metal oxides containing lithium (Li) can be mentioned. As the positive electrode active material, in addition to lithium (Li), a positive electrode active material containing at least one selected from the group consisting of cobalt (Co), nickel (Ni), manganese (Mn) and iron (Fe) is preferable. Examples of such positive electrode active materials include lithium-containing cobalt oxide (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium-containing nickel oxide (LiNiO ₂ ), and lithium-containing composite oxides of Co—Ni—Mn. , Ni—Mn—Al lithium-containing composite oxide, Ni—Co—Al lithium-containing composite oxide, olivine-type lithium manganese phosphate (LiMnPO ₄ ), olivine-type lithium iron phosphate (LiFePO ₄ ), Li _1+x Mn Lithium-rich spinel compounds represented by _2-x O ₄ (0<X<2), Li[Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ]O ₂ , LiNi _0.5 Mn _{1 .5} O ₄ and the like. In addition, one kind of positive electrode active material may be used alone, or two or more kinds may be used in combination at an arbitrary ratio.

The particle size of the electrode active material is not particularly limited, and may be the same as that of conventionally used electrode active materials.
Also, the amount of the electrode active material in the electrode slurry is not particularly limited, and can be within the conventionally used range.

<Conductive Material Dispersion>
As the conductive material dispersion, the conductive material dispersion of the present invention containing at least the fibrous conductive material described above, the polymer X described above, the nitrogen compound described above, and NMP is used.

<Other binders>
Other binders are not particularly limited, but fluoropolymers are preferable. Examples of the fluoropolymer include polyvinylidene fluoride (PVdF) and polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) copolymer. One type of fluoropolymer may be used alone, or two or more types may be used in combination at an arbitrary ratio. Among these, polyvinylidene fluoride is preferable from the viewpoint of further increasing the peel strength of the electrode and further suppressing an increase in internal resistance after cycling of the electrochemical device.

The content of the other binders in the electrode slurry is set to , preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, preferably 3 parts by mass or less, and more preferably 2 parts by mass or less.

<Method for preparing electrode slurry>
The method for preparing the electrode slurry is not particularly limited. The electrode slurry can be prepared by mixing the electrode active material, the conductive material dispersion, and other optional components such as a binder using, for example, a known mixing device. The electrode slurry can also be prepared without the conductive material dispersion liquid. may be prepared by

(electrode for electrochemical device)
The electrode of the present invention includes an electrode mixture layer obtained by using the electrode slurry of the present invention described above. More specifically, the electrode of the present invention usually comprises the above electrode mixture layer on a current collector. Further, in the electrode of the present invention, since the electrode mixture layer is formed from the electrode slurry of the present invention, it is possible to suppress an increase in internal resistance after cycling of the electrochemical device. Here, the electrode mixture layer is usually made of the dried electrode slurry of the present invention described above. The electrode mixture layer contains at least an electrode active material, a fibrous conductive material, a polymer X, and a nitrogen compound. The components contained in the electrode mixture layer are those contained in the electrode slurry of the present invention. is the same as the preferred abundance ratio of each component of

<Current collector>
The current collector is made of a material that is electrically conductive and electrochemically durable. The current collector is not particularly limited, and known current collectors can be used. For example, a current collector made of aluminum or an aluminum alloy can be used as the current collector included in the positive electrode of the lithium ion secondary battery. At this time, aluminum and an aluminum alloy may be used in combination, or aluminum alloys of different types may be used in combination. Aluminum and aluminum alloys are excellent current collector materials because they are heat resistant and electrochemically stable.

<Method for manufacturing electrode>
The method of manufacturing the electrode of the present invention is not particularly limited. For example, the electrode of the present invention can be produced by applying the electrode slurry of the present invention described above to at least one surface of a current collector and drying it to form an electrode mixture layer. More specifically, the manufacturing method includes a step of applying an electrode slurry to at least one surface of a current collector (application step), and drying the electrode slurry applied to at least one surface of the current collector. and a step of forming an electrode mixture layer on the current collector (drying step).

<< Coating process >>
The method for applying the electrode slurry onto the current collector is not particularly limited, and a known method can be used. Specifically, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, or the like can be used as the coating method. At this time, the electrode slurry may be applied to only one side of the current collector, or may be applied to both sides. The thickness of the slurry film on the current collector after application and before drying can be appropriately set according to the thickness of the electrode mixture layer obtained by drying.

<<Drying process>>
The method for drying the electrode slurry on the current collector is not particularly limited, and known methods can be used. drying method. By drying the electrode slurry on the current collector in this way, an electrode mixture layer can be formed on the current collector, and an electrode comprising the current collector and the electrode mixture layer can be obtained.

After the drying step, the electrode mixture layer may be pressurized using a mold press, a roll press, or the like. The pressure treatment allows the electrode mixture layer to adhere well to the current collector.
Furthermore, when the electrode mixture layer contains a curable polymer, the polymer may be cured after forming the electrode mixture layer.

(Electrochemical device)
The electrochemical device of the present invention comprises the electrode of the present invention described above. Since the electrochemical device of the present invention includes the electrode of the present invention, it is possible to suppress an excessive increase in internal resistance after cycles. The electrochemical device of the present invention is, for example, a nonaqueous secondary battery, preferably a lithium ion secondary battery.

Here, the configuration of a lithium ion secondary battery as an example of the electrochemical device of the present invention will be described below. This lithium ion secondary battery includes a positive electrode, a negative electrode, an electrolytic solution, and a separator. At least one of the positive electrode and the negative electrode is the electrode of the present invention. That is, in this lithium ion secondary battery, the positive electrode may be the electrode of the present invention and the negative electrode may be an electrode other than the electrode of the present invention, and the positive electrode may be an electrode other than the electrode of the present invention and the negative electrode may be the electrode of the present invention. and both the positive electrode and the negative electrode may be the electrodes of the present invention.

<Electrodes other than the electrodes of the present invention>
Electrodes that do not correspond to the electrodes of the present invention are not particularly limited, and known electrodes can be used.

<Electrolyte>
As the electrolytic solution, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. A lithium salt, for example, is used as the supporting electrolyte. Examples of lithium salts include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi. , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi and the like. Among them, LiPF ₆ , LiClO ₄ and CF ₃ SO ₃ Li are preferable, and LiPF ₆ is particularly preferable, because they are easily dissolved in a solvent and exhibit a high degree of dissociation. In addition, one electrolyte may be used alone, or two or more electrolytes may be used in combination at an arbitrary ratio. Generally, lithium ion conductivity tends to increase as a supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted depending on the type of supporting electrolyte.

The organic solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. Examples include dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), carbonates such as butylene carbonate (BC) and methyl ethyl carbonate (EMC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethylsulfoxide and the like are preferably used. A mixture of these solvents may also be used. Among them, carbonates are preferably used because they have a high dielectric constant and a wide stable potential range, and a mixture of ethylene carbonate and ethyl methyl carbonate is more preferably used.
The concentration of the electrolyte in the electrolytic solution can be adjusted as appropriate, for example, it is preferably 0.5 to 15% by mass, more preferably 2 to 13% by mass, and 5 to 10% by mass. is more preferred. Further, known additives such as fluoroethylene carbonate and ethyl methyl sulfone may be added to the electrolytic solution.

<Separator>
The separator is not particularly limited, and for example, those described in JP-A-2012-204303 can be used. Among these, the film thickness of the entire separator can be made thin, and as a result, the ratio of the electrode active material in the lithium ion secondary battery can be increased to increase the capacity per volume. Microporous membranes made of resins of the system (polyethylene, polypropylene, polybutene, polyvinyl chloride) are preferred.

<Method for manufacturing lithium ion secondary battery>
The lithium-ion secondary battery according to the present invention can be produced, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, winding or folding this according to the shape of the battery, if necessary, and placing it in a battery container. It can be produced by injecting an electrolytic solution into the container and sealing it. In order to prevent an increase in internal pressure of the secondary battery and the occurrence of overcharge/discharge, etc., a fuse, an overcurrent protection element such as a PTC element, an expanded metal, a lead plate, or the like may be provided as necessary. The shape of the secondary battery may be, for example, coin-shaped, button-shaped, sheet-shaped, cylindrical, rectangular, or flat.

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%", "ppm" and "parts" representing amounts are based on mass unless otherwise specified.
In addition, in a polymer produced by copolymerizing a plurality of types of monomers, the proportion of monomer units formed by polymerizing a certain monomer in the polymer is usually , coincides with the ratio (feed ratio) of the certain monomer to all the monomers used for the polymerization of the polymer. Further, when the polymer is a hydrogenated polymer obtained by hydrogenating a polymer containing aliphatic conjugated diene monomer units, unhydrogenated aliphatic conjugated diene monomer units in the hydrogenated polymer and the total content ratio of the alkylene structural unit as a hydrogenated aliphatic conjugated diene monomer unit is the ratio of the aliphatic conjugated diene monomer to the total monomers used in the polymerization of the polymer ( (stock ratio).
In Examples and Comparative Examples, various measurements and evaluations were performed by the following methods.

<Weight average molecular weight>
The weight average molecular weight of the polymer (Polymer X, polyvinylpyrrolidone) was determined by gel permeation chromatography (GPC). Specifically, the weight average molecular weight was calculated as a standard substance conversion value by creating a calibration curve using a standard substance using polystyrene. In addition, the measurement conditions are as follows.
<<Measurement conditions>>
Column: TSKgel α-M × 2 (inner diameter 7.8 mm × 30 cm × 2, manufactured by Tosoh Corporation)
Eluent: dimethylformamide (50 mM lithium bromide, 10 mM phosphoric acid)
Flow rate: 0.5 mL/min Sample concentration: about 0.5 g/L (solid content concentration)
Injection volume: 200 μL
Column temperature: 40°C
Detector: Differential refractive index detector RI (HLC-8320 GPC RI detector manufactured by Tosoh Corporation)
Detector conditions: RI: Pol (+), Res (1.0 s)
Molecular weight marker: standard polystyrene kit PStQuick K manufactured by Tosoh Corporation
<Iodine value>
The iodine value of the polymer was measured according to JIS K 6235.
<Sulfur content>
A NMP solution of the polymer was distilled under reduced pressure to remove the NMP to obtain a sample. About 0.02 g of a sample was weighed out on a magnetic board, burned in an automatic combustion device (manufactured by Yanaco), and then subjected to ion chromatography (manufactured by Metrohm, "930 Compact IC Flex") to quantify the sulfur content. The amount of sulfur contained was quantified as the amount (μg) of sulfur contained per 1 g of mass of the polymer, that is, the amount (ppm) based on the mass of the polymer.
<Surface acid content>
About 1 g of CNT to be measured is accurately weighed, and 0.01 mol dm ^-3 tetrabutyl hydride (also referred to as “tetrabutylammonium hydroxide”, hereinafter abbreviated as “TBA OH”)/4-methyl-2-pentanone. It was immersed in 100 ml of (MIBK) solution and stirred with a stirrer for 1 hour. After that, centrifugation was performed, and the supernatant was filtered through a filter. The TBA OH remaining in 50 mL of the obtained filtrate was quantitatively analyzed by non-aqueous coulometric titration with a 0.01 mol dm ⁻³ perchloric acid (HClO ₄ )/MIBK solution, and from the obtained value, The acid amount (mmol/g) was specified. For the analysis, an automatic coulometric titrator (manufactured by Kyoto Electronics Co., Ltd., product name "AT-700") was used. A series of operations were performed at room temperature under an argon stream.
<Amount of surface base>
About 1 g of CNT to be measured was precisely weighed, immersed in 100 ml of 0.01 mol dm ⁻³ HClO ₄ /MIBK solution, and stirred with a stirrer for 1 hour. After that, centrifugation was performed, and the supernatant was filtered through a filter. The remaining HClO ₄ in 50 mL of the obtained filtrate was quantitatively analyzed by non-aqueous coulometric titration with a 0.01 mol dm ⁻³ TBA OH/MIBK solution, and the amount of base per 1 g of CNT (mmol/ g) was identified. For the analysis, an automatic coulometric titrator (manufactured by Kyoto Electronics Co., Ltd., product name "AT-700") was used. A series of operations were performed at room temperature under an argon stream.
<BET specific surface area>
The BET specific surface area of CNT was measured using a Belsorp-mini (manufactured by Microtrac Bell, in accordance with ASTM D3037-81).
<D/G ratio>
The D/G ratio of CNTs was measured by fixing a sample under glass and using a Raman method (microscopic laser Raman SENTERRA manufactured by Bruker Optics) at an excitation wavelength of 532 nm.
<HSP distance>
The Hansen solubility parameter (HSP _N ) of the nitrogen compound, the Hansen solubility parameter (HSP _X ) of the polymer X, and the Hansen solubility parameter (HSP _F ) of the fibrous conductive material (CNT) are determined by the following method, and the above formula ( Using A) and ( _{B), the HSP distance (R A ) between the nitrogen compound and the polymer X and the HSP distance (R B )} between the nitrogen compound and the fibrous conductive material were calculated.
<<HSP _N of Nitrogen Compound>>
The numerical values (polar term δ _p1 , dispersion term δ _d1 and hydrogen bonding term δ _h1 ) described in the database of computer software “Hansen Solubility Parameters in Practice (HSPiP ver.5.3.06) were used. For substances that do not have a molecular breaking method, values obtained by the Y-MB method (Hiroshi Yamamoto's molecular breaking method) were used.
<< HSP _X of polymer X >>
0.5 g of polymer X was added to 10 ml of each of 15 kinds of organic solvents shown in Table 1, which will be described later, and the mixture was allowed to stand at 25° C. for 24 hours to prepare an evaluation solution. This evaluation liquid was visually observed and scored as follows.
・ Insoluble (poor solvent): 0
・ Turbidity and / or fluctuation state (poor solvent): 2
・Complete dissolution (good solvent): 1
The results of scoring are shown in Table 1. According to the scores obtained, the polar term δ _p2 , the dispersion term δ _d2 and the hydrogen bonding term δ _h2 of HSP _X were determined using the above HSPiP calculation program. For the polyvinylpyrrolidone (PVP) used in Comparative Example 3, the numerical values of the HSPiP database were used.
<< HSP _F of fibrous conductive material >>
0.1 g of a fibrous conductive material (CNT) was added to 10 ml of each of 16 types of organic solvents shown in Table 2, which will be described later, and ultrasonically dispersed at 20 kHz, 200 W, and 10 minutes to obtain a measurement solution. A pulse NMR measurement was performed on the 16 types of organic solvents (pure solvents) and the measurement solution described above. From the obtained results, R _sp as a function of the relaxation time T1 of the pure solvent and the relaxation time T2 of the solvent in the measurement solution was calculated using the following formula.
_Rsp = (T1/T2)-1
Based on the obtained R _sp value, the affinity between each solvent and the fibrous conductive material was scored as follows.
・R _sp ≦0.2 (poor solvent): 0
· 0.2 < R _sp ≤ 0.5 (poor solvent): 2
・0.5<R _sp (good solvent): 1
Scoring results are shown in Table 2. According to the scores obtained, the polar term δ _p3 , the dispersion term δ _d3 and the hydrogen bonding term δ _h3 of HSP _F were determined using the above HSPiP calculation program.
<Effect of reducing viscosity>
The effect of reducing the viscosity of the combination of the nitrogen compound or the like and the polymer X or the like used in each of Examples and Comparative Examples was evaluated as follows.
First, an 8% NMP solution of polymer X etc. was prepared. The viscosity (V ₁ ) of this NMP solution was measured at 25° C. using a Brookfield viscometer (rotation speed: 60 rpm).
Next, an 8% NMP solution of polymer X or the like and a separately prepared 8% NMP solution of nitrogen compound or the like are mixed at a mass ratio of polymer X or the like: nitrogen compound or the like = 1:9, and a shaker is added. was stirred at 60 rpm for 1 hour to prepare a sample solution. The viscosity (V ₂ ) of this sample liquid was measured at 25° C. using a Brookfield viscometer (rotation speed: 60 rpm).
Then, the viscosity ratio (%)=V ₂ /V ₁ ×100 was calculated and evaluated according to the following criteria. The smaller the value of the viscosity ratio before and after the addition of the nitrogen compound or the like, the better the viscosity reduction effect due to the addition of the nitrogen compound or the like.
A: Viscosity ratio less than 60% B: Viscosity ratio 60% or more and less than 65% C: Viscosity ratio 65% or more <dispersion initial viscosity (dispersibility)>
The dispersion initial viscosity η _A of the conductive material dispersion was measured using a rheometer (MCR302 manufactured by Anton Paar) under conditions of a temperature of 25° C. and a shear rate of 10 s ⁻¹ and evaluated according to the following criteria. The smaller the value of _ηA , the better the CNTs and the like are dispersed in the conductive material dispersion.
A: η _A is 5 Pa s or less B: η _A is more than 5 Pa s and 15 Pa s or less C: η _A is more than 15 Pa s and 50 Pa s or less D: η _A is more than 50 Pa s, or measurement is not possible <dispersion property (dispersion initial TI value)>
For the conductive material dispersion, using a rheometer (MCR302 manufactured by Anton Paar) at a temperature of 25 ° C., shear rate dependence of viscosity in the range of 10 ^-2 to 10 ³ in units of 1 / s. evaluated the sex. Then, using the viscosity η ₁₀ at a shear rate of 10 s ⁻¹ and the viscosity η _0.1 at a shear rate of 0.1 s ⁻¹ , the TI value = η _0.1 /η ₁₀ was calculated and evaluated according to the following criteria. . A lower TI value indicates better dispersion of CNTs and the like in the conductive material dispersion.
A: TI value less than 30 B: TI value 30 or more and less than 50 C: TI value 50 or more and less than 70 D: TI value 70 or more <Temporal stability of electrode slurry>
For the electrode slurry, the viscosity value V _1h after 1 hour of preparation and the viscosity value V _10d after 10 days of preparation were measured. Each viscosity was measured using a Brookfield viscometer (rotation speed: 60 rpm) at a temperature of 25°C.
Then, viscosity increase rate (%)=(V _10d −V _1h )/V _1h was calculated and evaluated according to the following criteria. The smaller the value of the viscosity increase rate, the more difficult it is for the electrode slurry to thicken over time.
A: Viscosity increase rate of less than 20% B: Viscosity increase rate of 20% or more and less than 50% C: Viscosity increase rate of 50% or more <Suppression of resistance increase after cycle>
A lithium ion secondary battery was charged to 50% of SOC (State Of Charge, depth of charge) at 1C (C is a numerical value represented by rated capacity (mA)/1 hour (h)) in an atmosphere of 25°C. . After that, in an environment of 25 ° C., charging was performed for 20 seconds and discharging was performed for 20 seconds at 0.2 C, 0.5 C, 1.0 C, 2.0 C, and 3.0 C centering on 50% of SOC. Plot the battery voltage after 20 seconds in the case (charging side and discharging side) against the current value, obtain the slope as IV resistance (Ω) (IV resistance during charging and IV resistance during discharging), IV resistance before cycle R ₁ (Ω).
After that, the lithium ion secondary battery was charged at 1C to a battery voltage of 4.2 V and discharged at 1 C to a battery voltage of 3.0 V in an atmosphere of 45° C., and the operation was repeated 200 times to carry out a cycle test. .
Then, the IV resistance (Ω) was obtained by the same method as above, and was defined as the post-cycle IV resistance R ₂ (Ω).
For the obtained IV resistance R ₂ (Ω) after the cycle, IV resistance increase rate (%) based on the IV resistance R ₁ (Ω) before the cycle = (R ₂ - R ₁ )/R ₁ × 100 Calculated. Based on this IV resistance increase rate (%) and the IV resistance R ₂ (Ω) after the cycle, evaluation was made according to the following criteria.
The smaller the IV resistance increase rate (%) and the IV resistance R ₂ (Ω) after the cycle test, the longer the resistance is reduced, and the better the battery characteristics of the lithium ion secondary battery.
A: IV resistance increase rate is less than 30% and _R2 is less than 2.5Ω B: IV resistance increase rate is 30% or more and less than 35% and _R2 is less than 2.8Ω C: IV resistance increase rate is 35% or more 40 % and R ₂ is less than 3.2Ω D: IV resistance change rate is 40% or more

(Example 1)
<Preparation of polymer X>
A reactor was charged with 200 parts of ion-exchanged water, 25 parts of a 10% concentration sodium dodecylbenzenesulfonate aqueous solution, 35 parts of acrylonitrile as a nitrile group-containing monomer, and 7.90 parts of t-dodecylmercaptan as a molecular weight modifier. The parts were prepared in this order. Then, after replacing the internal gas with nitrogen three times, 65 parts of 1,3-butadiene as an aliphatic conjugated diene monomer was charged. Then, the reactor was kept at 5° C., 0.03 parts of cumene hydroperoxide as a polymerization initiator, a reducing agent, and an appropriate amount of a chelating agent were charged, and the polymerization reaction was continued while stirring until the polymerization conversion rate reached 80%. When the temperature became low, 0.1 part of an aqueous solution of hydroquinone having a concentration of 10% was added as a polymerization terminator to terminate the polymerization reaction. Subsequently, residual monomers were removed at a water temperature of 80° C. to obtain an aqueous dispersion of a polymer precursor.
In an autoclave, an aqueous dispersion and a palladium catalyst (1% palladium acetate acetone solution and an equal weight of A solution mixed with ion-exchanged water) is added, and a hydrogenation reaction is performed at a hydrogen pressure of 3 MPa and a temperature of 50° C. for 6 hours to obtain an aqueous dispersion of the desired polymer X (hydrogenated polymer, hydrogenated nitrile rubber). Obtained.
After that, the contents were returned to normal temperature, the inside of the system was made into a nitrogen atmosphere, and then concentrated to a solid content concentration of 40% using an evaporator to obtain a concentrate of an aqueous dispersion.
Next, 200 parts of NMP was added to 100 parts of the concentrate of this aqueous dispersion, water and residual monomers were all evaporated under reduced pressure, and then NMP was evaporated to obtain 7 of polymer X (X-1). A .2% NMP solution was obtained.
The iodine value, weight average molecular weight and sulfur content of this polymer X were measured. Table 3 shows the results.
<Preparation of binder composition>
A binder composition was prepared by adding 2-methyl-2-imidazoline (molecular weight: 84, polarity term δ _p1 : 10.5 MPa ^1/2 ) as a nitrogen compound to the NMP solution of polymer X obtained as described above. . The amount of 2-methyl-2-imidazoline added was such that the polymer X (solid content equivalent):2-methyl-2-imidazoline=90:10 (based on mass).
Separately, the viscosity reducing effect was evaluated using the polymer X and 2-methyl-2-imidazoline. Also, the HSP distance (R _A ) between the nitrogen compound and the polymer X was calculated. Table 3 shows the results.
<Preparation of surface-treated CNT>
1 g of weighed multi-walled carbon nanotubes (BET specific surface area: 300 m ² /g) was added to a mixed solution of 40 mL of concentrated nitric acid and 40 mL of 2M sulfuric acid, and stirred for 1 hour while being kept at 60° C. (acid treatment). Then, it was filtered using a filter paper (Toyo Roshi Kaisha, Filter Paper No. 2, 125 mm) for solid-liquid separation. After washing the solid matter on the filter paper with 200 ml of purified water, the CNT solid matter (acid-treated CNT) was recovered. Further, this CNT solid was put into 200 ml of an aqueous lithium hydroxide solution having a concentration of 2.5 mol/liter, and then stirred for 2 hours while being kept at 25° C. in a water bath (base treatment). Thereafter, a membrane filter with a pore size of 10 μm was used to carry out suction filtration for solid-liquid separation. The CNT solids (acid-base-treated CNTs) on the membrane filter were repeatedly washed with purified water. When the electrical conductivity of the washing water became 50 μs/m or less, the solid-liquid separation of the CNT solids was performed in the same manner as above. The obtained CNT solid was dried under reduced pressure at 50° C. for 8 hours to prepare surface-treated CNT (C-1). Table 3 shows the surface acid content of this surface-treated CNT, the ratio of the surface acid content to the surface base content, and the D/G ratio. The BET specific surface area of this surface-treated CNT was 300 m ² /g.
<Preparation of conductive material dispersion>
6.0 parts of the surface-treated CNT as a fibrous conductive material, 1.2 parts of the binder composition (in terms of solid content), and 92.8 parts of NMP were stirred using a disper (3000 rpm, 10 minutes). After that, using a bead mill using zirconia beads with a diameter of 1 mm, the mixture was mixed at a peripheral speed of 8 m/sec for 1 hour to produce a conductive material dispersion having a solid concentration of 7.2%. The initial dispersion viscosity and the initial dispersion TI value of this conductive material dispersion were evaluated. Table 3 shows the results.
Also, the HSP distance (R _B ) between the nitrogen compound and the fibrous conductive material was calculated. Table 3 shows the results.
<Preparation of positive electrode slurry>
1.0 parts of the conductive material dispersion obtained as described above (in terms of solid content) and a ternary active material having a layered structure as a positive electrode active material (LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , volume average Particle diameter: 10 μm) 98.0 parts, 1.0 parts of polyvinylidene fluoride as another binder, and NMP were mixed in a planetary mixer (60 rpm, 30 minutes) to obtain a positive electrode slurry. prepared. The amount of NMP added is such that the viscosity of the obtained positive electrode slurry (measured with a single cylindrical rotational viscometer according to JIS Z8803: 1991; temperature: 25°C, rotation speed: 60 rpm) is 4000 to 5000 mPa s. Adjusted to be within range.
<Preparation of positive electrode>
An aluminum foil having a thickness of 20 μm was prepared as a current collector. The positive electrode slurry obtained as described above was applied to one side of an aluminum foil with a comma coater so that the weight per unit area after drying was 20 mg/cm ² . After drying at 90°C for 20 minutes and at 120°C for 20 minutes, A heat treatment was performed at 60° C. for 10 hours to obtain a positive electrode material. This positive electrode raw material was rolled by a roll press to produce a sheet-like positive electrode comprising a positive electrode mixture layer (density: 3.2 g/cm ³ ) and an aluminum foil. Then, the sheet-like positive electrode was cut into a width of 48.0 mm and a length of 47 cm to obtain a positive electrode for a lithium ion secondary battery.
<Production of negative electrode>
In a 5 MPa pressure vessel equipped with a stirrer, 33 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 3.5 parts of itaconic acid as a carboxylic acid group-containing monomer, and styrene as an aromatic-containing monomer 63.5 parts, 0.4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 parts of potassium persulfate as a polymerization initiator were added, stirred sufficiently, and then heated to 50°C. Polymerization was initiated by warming. When the polymerization conversion rate reached 96%, the mixture was cooled to terminate the polymerization reaction to obtain a mixture containing a particulate binder (styrene-butadiene copolymer). After adjusting the pH to 8 by adding a 5% sodium hydroxide aqueous solution to the above mixture, unreacted monomers were removed by heating under reduced pressure distillation. After that, the mixture was cooled to 30° C. or less to obtain an aqueous dispersion containing the negative electrode binder.
A planetary mixer was charged with 48.75 parts of artificial graphite and 48.75 parts of natural graphite as negative electrode active materials, and 1 part of carboxymethyl cellulose (equivalent to solid content) as a thickener. Further, the mixture was diluted with ion-exchanged water to a solid content concentration of 60%, and then kneaded at a rotation speed of 45 rpm for 60 minutes. After that, 1.5 parts of the aqueous dispersion containing the negative electrode binder obtained as described above was added in terms of the solid content, and kneaded at a rotation speed of 40 rpm for 40 minutes. Then, ion-exchanged water was added so that the viscosity was 3000±500 mPa·s (measured with a Brookfield viscometer at 25° C. and 60 rpm) to prepare a negative electrode slurry.
The negative electrode slurry was applied to the surface of a copper foil having a thickness of 15 μm as a current collector with a comma coater so that the coating amount was 10±0.5 mg/cm ² . After that, the copper foil coated with the negative electrode slurry was conveyed at a speed of 400 mm/min in an oven at a temperature of 80° C. for 2 minutes and then in an oven at a temperature of 110° C. for 2 minutes. The slurry was dried to obtain a negative electrode raw sheet in which a negative electrode mixture layer was formed on a current collector.
This negative electrode material was rolled by a roll press to produce a sheet-like negative electrode comprising a negative electrode mixture layer (density: 1.6 g/cm ³ ) and aluminum foil. Then, the sheet-shaped negative electrode was cut into a width of 50.0 mm and a length of 52 cm to obtain a negative electrode for a lithium ion secondary battery.
<Production of lithium ion secondary battery>
The positive electrode for a lithium ion secondary battery and the negative electrode for a lithium ion secondary battery that were prepared are arranged so that the electrode mixture layers face each other, and a separator (polyethylene microporous film) having a thickness of 15 μm is interposed to form a separator having a diameter of 20 mm. It was wound using a core to obtain a wound body. Then, the obtained wound body was compressed in one direction at a speed of 10 mm/sec until the thickness became 4.5 mm. The wound body after compression had an elliptical shape in plan view, and the ratio of the major axis to the minor axis (major axis/minor axis) was 7.7.
In addition, a _LiPF6 solution with a concentration of 1.0 M as an electrolytic solution (solvent: mixed solvent of ethylene carbonate (EC)/ethyl methyl carbonate (EMC) = 3/7 (volume ratio), additive: vinylene carbonate 2% by volume (solvent ratio) containing) was prepared.
Thereafter, the wound body after compression was placed in an aluminum laminate case together with 3.2 g of electrolyte. A nickel lead wire is connected to a predetermined portion of the negative electrode, and an aluminum lead wire is connected to a predetermined portion of the positive electrode. I got the following battery. This lithium ion secondary battery was a pouch-shaped battery with a width of 35 mm, a height of 60 mm, and a thickness of 5 mm, and the nominal capacity of the battery was 700 mAh.
The resulting lithium ion secondary battery was evaluated for resistance increase suppression after cycling. Table 3 shows the results.

(Examples 2 and 3)
DBU (Example 2, molecular weight: 152, polarity term δ _p1 : 6.4 MPa ^1/2 ), TBD (Example 3. Polymer X, binder composition, surface-treated _CNT , conductive material ^dispersion , positive electrode A slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were produced, and various evaluations were performed. Table 3 shows the results.

(Example 4)
The same as in Example 1, except that the amount of t-dodecylmercaptan used as a molecular weight modifier was adjusted (reduced) to change the weight-average molecular weight and sulfur content of polymer X in the preparation of polymer X. Polymer X (X-4), binder composition, surface-treated CNT, conductive material dispersion, positive electrode slurry, positive electrode, negative electrode, and lithium ion secondary battery were produced and various evaluations were performed. Table 3 shows the results.

(Example 5)
Polymer X (X-5), binder composition, surface A treated CNT, a conductive material dispersion, a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were produced, and various evaluations were performed. Table 3 shows the results.

(Examples 6 and 7)
In the preparation of polymer X, after reducing the amount of acrylonitrile to 25 parts, 10 parts of n-butyl acrylate (Example 6) as a (meth)acrylic acid ester monomer, respectively, as an aromatic-containing monomer Polymer X (Example 6: X-6, Example 7: X-7), binder composition, surface-treated CNT , a conductive material dispersion, a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared, and various evaluations were performed. Table 3 shows the results.

(Example 8)
When preparing the binder composition, the amount of 2-methyl-2-imidazoline added was changed to the amount of polymer X (solid content equivalent): 2-methyl-2-imidazoline = 65:35 (based on mass). Polymer X, binder composition, surface-treated CNTs, conductive material dispersion, positive electrode slurry, positive electrode, negative electrode, and lithium ion secondary battery were prepared in the same manner as in Example 1 except that they were subjected to various evaluations. Table 3 shows the results.

(Examples 9 and 10)
The same as in Example 1 except that the surface acid amount, the surface base amount, and the D/G ratio of the surface-treated CNT obtained by adjusting the base treatment time and the acid treatment time were changed in preparing the surface-treated CNT. Then polymer X, binder composition, surface-treated CNT (Example 9: C-9, Example 10: C-10), conductive material dispersion, positive electrode slurry, positive electrode, negative electrode and lithium ion secondary battery It was produced and various evaluations were performed. Table 4 shows the results.

(Example 11)
Binder composition, surface-treated CNT, conductive material dispersion, positive electrode slurry, positive electrode, negative electrode and A lithium ion secondary battery was produced and various evaluations were performed. Table 4 shows the results.
<Preparation of polymer X>
[Polymerization (preparation of polymer intermediate)]
A reactor was charged with 180 parts of ion-exchanged water, 25 parts of a 10% concentration sodium dodecylbenzenesulfonate (emulsifier) aqueous solution, 35 parts of acrylonitrile as a nitrile group-containing monomer, and t-dodecylmercaptan as a molecular weight modifier. After replacing the internal gas with nitrogen three times, 65 parts of 1,3-butadiene as an aliphatic conjugated diene monomer was charged. Then, the reactor was kept at 10° C., 0.1 part of cumene hydroperoxide (polymerization initiator) and 0.1 part of ferrous sulfate were charged, and the polymerization reaction was continued while stirring. When the polymerization conversion reached 85%, 0.1 part of an aqueous hydroquinone solution (polymerization terminator) having a concentration of 10% was added to terminate the polymerization reaction. Then, residual monomers were removed at a water temperature of 80° C. to obtain a latex of nitrile rubber. A portion of the obtained latex was added to an aqueous solution of magnesium sulfate in an amount of 12% with respect to the nitrile rubber content, and the mixture was stirred to coagulate the latex. Thereafter, it was washed with water and separated by filtration, and the obtained coagulate was vacuum-dried at a temperature of 60° C. for 12 hours to obtain a nitrile rubber, which is an intermediate of the target polymer (polymer intermediate).
[Metathesis of polymer intermediate]
Next, 9 parts of the obtained nitrile rubber was dissolved in 141 parts of monochlorobenzene and charged into the reactor. Then, after heating the reactor to 80° C., 2 L of a monochlorobenzene solution containing bis(tricyclohexylphosphine)benzylidene ruthenium dichloride as a Grubbs catalyst is added so that the amount of the Grubbs catalyst is 0.25 parts per 100 parts of the polymer. added like Then, the inside of the reactor was pressurized to 3.5 MPa with ethylene as a coolefin, and the metathesis reaction of the nitrile rubber was carried out at a stirring speed of 600 rpm. The temperature was kept constant during the reaction using a temperature controller and a cooling coil connected to a thermal sensor.
[Hydrogenation of Metathesis Polymer Intermediate]
After that, the inside of the reactor was degassed three times with 0.7 MPa of H ₂ while stirring was continued. The temperature of the reactor was then raised to 130° C. and 1 L of the monochlorobenzene solution containing Wilkinson's catalyst and triphenylphosphine was added to the reactor. The amount of Wilkinson's catalyst was 0.075 parts and the amount of triphenylphosphine was 1 part per 100 parts of the metathesis-completed polymer intermediate. Then, the temperature was raised to 138° C. and hydrogenation reaction of the polymer was carried out for 6 hours under the condition of hydrogen pressure of 8.4 MPa to obtain a hydrogenated polymer. After completion of the reaction, 0.2 part of activated carbon with an average diameter of 15 μm was added to the reactor and stirred for 30 minutes. After that, it was filtered through a filter with a pore size of 5 μm to obtain a filtered solution.
[Preparation of NMP composition]
50 parts of the hydrogenated polymer obtained as described above (equivalent to 3 parts as solid content) were sampled and mixed with 17 parts of NMP to obtain a mixed solution. Then, all of the monochlorobenzene contained in the resulting mixture was evaporated under reduced pressure to obtain a 7.2% NMP solution of polymer X (X-11).

(Examples 12 and 13)
Example except that C-9 (Example 12) and C-10 (Example 13) obtained in the same manner as in Examples 9 and 10 were used as the surface-treated CNTs when preparing the conductive material dispersion. A polymer X, a binder composition, a conductive material dispersion, a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in 11, and various evaluations were performed. Table 4 shows the results.

(Comparative Examples 1 and 2)
In preparing the binder composition, benzoic acid (Comparative Example 1, molecular weight: 122, polarity term δ _p1 : 6.9 MPa ^1/2 ) and 2-methylimidazole were used instead of 2-methyl-2-imidazoline as nitrogen compounds. (Comparative Example 2, molecular weight: 82, polar term δ _p1 : 12.0 MPa ^1/2 ) was used in the same manner as in Example 1 to obtain the polymer X, the binder composition, the surface-treated CNT, and the conductive material dispersion. , a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared and various evaluations were performed. Table 4 shows the results.

(Comparative Example 3)
In the preparation of the binder composition, the binder composition, the surface-treated CNT, the conductive material dispersion, the positive electrode slurry, the positive electrode, the negative electrode and lithium were prepared in the same manner as in Example 1, except that polyvinylpyrrolidone was used instead of the polymer X. An ion secondary battery was produced and various evaluations were performed. Table 4 shows the results.

In addition, in Tables 3 and 4 shown below,
"AN" means acrylonitrile unit;
"BD" means a structural unit derived from 1,3-butadiene (1,3-butadiene unit and/or 1,3-butadiene hydride unit),
"BA" means n-butyl acrylate units;
"ST" means styrene units;
"PVP" means polyvinylpyrrolidone;
"Mw" means weight average molecular weight;
"25k" means 25 x 103, " ^250k " means 250 x 103 ^,
"MI" means 2-methyl-2-imidazoline;
"DBU" means diazabicycloundecene;
"TBD" means 1,5,7-triazabicyclo[4.4.0]dec-5-ene;
"MIZ" means 2-methylimidazole.

From Tables 3 and 4, Examples 1 to 13 containing a predetermined polymer X, a predetermined nitrogen compound, and NMP, and having an HSP distance (R _A ) between the nitrogen compound and the polymer X of 10.0 MPa ^1/2 or less According to the above, it is possible to produce a positive electrode that allows the electrochemical device to exhibit excellent cycle characteristics.

According to the present invention, a binder composition for an electrochemical element capable of forming an electrode capable of suppressing an increase in internal resistance after cycling of the electrochemical element, a conductive material dispersion for an electrochemical element, and a slurry for an electrochemical element electrode can be provided.
Moreover, according to the present invention, it is possible to provide an electrochemical device in which an increase in internal resistance after cycles is suppressed.

Claims (14)

A binder composition for an electrochemical element comprising a polymer X, N-methyl-2-pyrrolidone, and a nitrogen compound other than the N-methyl-2-pyrrolidone,
The polymer X contains a nitrile group-containing monomer unit and contains at least one of an aliphatic conjugated diene monomer unit and an alkylene structural unit,
The nitrogen compound has a molecular weight of 1,000 or less,
And, the HSP distance (R _A ) between the Hansen solubility parameter (HSP _N ) of the nitrogen compound and the Hansen solubility parameter (HSP _X ) of the polymer X is 10.0 MPa ^1/2 or less, for an electrochemical device binder composition. The binder composition for electrochemical elements according to claim 1, wherein the polymer X has a weight average molecular weight of 300,000 or less. The binder composition for an electrochemical element according to claim 1, wherein the polymer X has a sulfur content of 500 ppm by mass or more. The binder composition for electrochemical elements according to claim 1, wherein the polar term _δp1 in the Hansen solubility parameter (HSP _N ) of the nitrogen compound is 14.0 MPa ^1/2 or less. The binder composition for electrochemical elements according to claim 1, wherein the nitrogen compound has a cyclic amidine structure. 2. The binder composition for an electrochemical element according to claim 1, wherein the mass ratio of said nitrogen compound in the total mass of said polymer X and said nitrogen compound is 0.1% by mass or more and 40% by mass or less. A conductive material dispersion for electrochemical elements, comprising the binder composition for electrochemical elements according to claim 1 and a fibrous conductive material. The conductive material dispersion for an electrochemical device according to claim 7, wherein the fibrous conductive material is a bundle type. The conductive material dispersion for an electrochemical device according to claim 7, wherein the fibrous conductive material has a surface acidity of 0.01 mmol/g or more and 0.20 mmol/g or less. 8. The electrochemical device according to claim 7, wherein the fibrous conductive material is a fibrous carbon material, and the ratio of the D band peak intensity to the G band peak intensity in the Raman spectrum of the fibrous carbon material is 2.0 or less. conductive material dispersion. A slurry for electrochemical element electrodes, comprising the conductive material dispersion for electrochemical elements according to claim 7 and an electrode active material. The slurry for an electrochemical element electrode according to claim 11, further comprising a binder other than the polymer X. An electrode for an electrochemical element, comprising an electrode mixture layer formed using the slurry for an electrochemical element electrode according to claim 11 or 12. An electrochemical device comprising the electrode for an electrochemical device according to claim 13.